Development work of electrically powered vehicles such as electric cars and hybrid cars has been pursued vigorously in recent years. There is an increasing need for secondary batteries with excellent performance, reliability, and safety as driving or auxiliary power sources used in the electrically powered vehicles.
The driving or auxiliary power sources of the electrically powered vehicles require high power density. As one example, a electric power storage apparatus is used which has a container for accommodating an assembled battery including a plurality of unit cells connected in series and/or in parallel and a coolant for cooling the assembled battery.
The container is formed of a container body having side walls and a bottom wall which are integrally formed and an upper case for sealing the container body. The upper case is fixed to the container body via a fastening member.
Each of the unit cells has a gas release valve for letting out gas produced from electrolysis of an electrolyte due to overcharge. The gas release valve allows the release of the gas to prevent an extreme increase in internal pressure of each unit cell.
Patent Document 1 has disclosed a battery housing case which includes a casing having a generally flat shape for housing a laminate sheathed battery in a sealed state, a concave portion having a recessed shape in section bowed inward in the surface of the casing, and a rupture valve placed in a bottom wall surface having the concave portion formed therein, the rupture valve serving as a gas release mechanism for releasing gas ejected from the laminate sheathed battery in the casing to the outside of the casing at the time of an abnormality.
Patent Document 2 has disclosed a cylindrical battery in which small gas-release holes are formed in a unit cell housed in an exterior case and in a cylindrical portion of the exterior case that abuts on the unit cell. High-pressure gas ejected from the unit cell is released from the exterior case through the gas-release holes.
Patent Document 3 has disclosed a battery module in which a plurality of fillers made of materials having different properties are provided between a set of unit cells and a battery case, a low-temperature filler of the fillers that has the lowest flow start temperature is placed near a battery sheath, and upon generation of gas, the low-temperature filler is caused to flow to form space for expansion to ensure release of the gas from near the battery sheath into outside space.    [Patent Document 1] Japanese Patent Laid-Open No. 2005-129487    [Patent Document 2] Laid-open Japanese Utility Model Registration Application No. 05 (1993)-65054    [Patent Document 3] Japanese Patent Laid-Open No. 2003-272588